The annual worldwide consumption of asphalt for road surfacing applications exceeds 90,000,000 tons. Europe and North America are responsible for approximately two thirds of this consumption. In the United States more than four million miles of roads are paved with asphalt. Asphalt pavement deteriorates with use, due to oxidation of asphalt binder, high loads and varying climatic conditions. A recent study demonstrates a statistically significant relationship between a country's economic development and its road infrastructure1 Accordingly, maintenance and rejuvenation of asphalt surfaced roads is a matter of some importance. In developed countries it is understood that preventative maintenance of existing roadways is preferable to replacement2. Accordingly, improvement in the technology for maintaining existing roadways is desirable. 1 C. Queroz, R. Haas, and Y Cai, “National Economic Development and Prosperity Related to Paved Road Infrastructure” Transportation Research Record, 1455 (1994).2 M. S. Mamlouk and J. P. Zaniewske, “Pavement Preventive Maintenance: Description, Effectiveness, and Treatments”, Symposium on Flexible Pavement Rehabilitation and Maintenance, ASTM STP 1349, 121-135, 1999.
Asphalt road surfaces typically consist of asphalt and aggregate. Oxidation of asphalt binder during its service time, climate conditions and use of road surfaces, particularly by heavy loads, result in deterioration of the road surfaces over time. For example, repeated contraction of the road surface during the cold winter nights due to temperature changes results in formation of perpendicular cracks in pavement, known as cold fractures. The asphalt binder becomes too soft during the hot summer days, resulting in a permanent deformation of the road surface under repeated heavy loads, termed “rutting”. In addition, as a result of continuous mechanical stress, road surfaces become fatigued, resulting in formation of alligator skin-like cracks, known as fatigue fracture.
One approach to the progressive deterioration of asphalt pavement is to remove and replace the existing pavement with either newly prepared or recycled pavement. However, removal and replacement is expensive and wasteful3. A preferable approach involves surface treatment of the existing pavement to restore the pavement to its condition when first laid down4. For example, U.S. Pat. No. 5,180,428 to Richard D. Koleas discloses a composition including asphalt, a recycling agent, a polymer and an emulsifying agent in an aqueous solution that when deposited upon aged and cracked asphalt pavement rejuvenates the pavement by replenishing solvent oils (maltenes) driven off by wear and exposure to the elements. The '428 patent is expressly incorporated herein by reference. 3 F. L. Roberts, P. S. Kandhal, E. R. Brown, D. Y. Lee, T. W. Kennedy, “Hot Mix Asphalt Materials, Mixture Design and Construction”, NAPA Research and Education Foundation Textbook, 2nd Edition, 1999.4 K. Takamura, K. P. Lok, R. Wittlinger, “Microsurfacing for Preventive Maintenance: Eco-Efficient Strategy”, ISSA Annual Meeting, March 2001.
The invention of the '428 patent is sold under the mark “PASS.” PASS is also used as a tack coat, chip seal, scrub seal and fog seal as well as for crack filling. An advantage of PASS is that it can be applied in a single step, over existing pavement. Moreover, PASS rejuvenates and prevents further oxidation of the underlying pavement. Moreover, PASS can be applied over a wide temperature range.
Recent studies of the mechanism by which PASS acts on pavement confirm that it rejuvenates old asphalt by restoring the aromatic content of the asphalt in the underlying pavement, and forms a polymer rich, thin, stress absorbing membrane, which strongly adheres to the underlying pavement. Thus PASS prevents reflective crack formation when other types of the surface treatment (i.e, microsurfacing and slurry seal) are applied on the PASS treated pavement.